(1) Field of the Invention
The present application relates to restricting the transfer of a fluid from between two pressurized chambers, and more specifically to a reverse flow tolerant brush seal for restricting the transfer of pressurized air between chambers in various gas turbine engine applications.
(2) Description of the Related Art
Gas turbine engines operate according to a continuous-flow, Brayton cycle. A forward compressor section pressurizes ambient air, fuel is added and the pressurized mixture is burned in a central combustor section. The combustion gases expand through a rearward turbine section before a rearmost nozzle expels the gases as a propulsive jet. Bladed rotors in the turbine section convert thermodynamic energy from the combustion gases into mechanical energy for rotating one or more centrally mounted shafts. The shafts, in turn, drive the forward compressor section, thus continuing the cycle. Gas turbine engines are compact and efficient power plants for powering aircraft, heavy equipment, waterborne vehicles and electrical power generators.
The interfaces between adjacent engine components are sealed in various ways to restrict leakage of fluids such as the pressurized compressor air and combustion gases. There are many interfaces between rotating and stationary components in a gas turbine engine. Sealing these interfaces presents challenges due to the excessive fluid temperatures and pressures, combined with relative axial and/or radial movement between the engine components.
Brush seals, such as disclosed in U.S. Pat. No. 6,910,857, Ser. No. 10/330,751, to Addis, provide a restriction to fluid leakage between components that are subject to relative axial and/or radial movement. Bristles with flexible ends bridge a gap between adjacent components and any relative movement is absorbed through deflection of the bristles. The tortuous path through the bristles achieves the restriction effect even as the gap distance changes.
Brush seal bristles are also susceptible to deflection due to fluid pressure loading. For this reason, back plates and side plates support the bristles along a majority of their length. The bristles are loaded against the back plate by the fluid pressure, thus preventing permanent deflection. The side plates are scalloped where they contact the bristles to provide a space for bristle flexure and to allow any frictional heat to dissipate out of the bristles.
An undesirable consequence of the side plate scallop is the reduced support it provides the bristle ends. For this reason, brush seals are designed to have the bristles continuously loaded in one direction, against the back plates. Brush seals are used in applications where a continuous pressure differential exists. If a brush seal is installed in reverse or an unanticipated flow reversal occurs, the unsupported bristles will deflect under pressure. Bristle deflections eventually yield the bristle ends, reducing their sealing effectiveness and rendering them unacceptable for continued service. Reduced brush seal effectiveness will increase fluid leakage, engine fuel burn and, in turn, reduce an operator's profit until the brush seal is replaced. Removal and disassembly of a gas turbine engine for brush seal replacement is both costly and time consuming.
Experience shows that flow reversals can occur under certain gas turbine operating conditions, thus precluding the use of brush seals in certain applications. A brush seal that is tolerant of flow reversals is presently needed.